The vibrating object creates compressions and rarefactions in the medium. These pressure variations travel through the medium as a wave. When this wave reaches our ear, it causes our eardrum to vibrate, which our brain interprets as sound.
When the school bell is struck, it vibrates. These vibrations create compressions and rarefactions in the surrounding air, which propagate as sound waves that travel to our ears.
Sound waves are called mechanical waves because they require a material medium (solid, liquid, or gas) for propagation. They involve the physical movement of particles in the medium.
No, because sound requires a medium to travel, and the moon has no atmosphere (it's a vacuum). Without a medium, sound waves cannot propagate.
(a) Amplitude determines loudness
(b) Frequency determines pitch
A guitar typically has a higher pitch than a car horn. Guitar strings vibrate at higher frequencies, producing higher-pitched sounds.
- Wavelength: Distance between two consecutive compressions or rarefactions
- Frequency: Number of oscillations per unit time
- Time period: Time taken for one complete oscillation
- Amplitude: Maximum displacement of particles from their mean position
Speed of sound (v) = Wavelength (λ) × Frequency (ν)
v = λν
Using the formula: v = λν
λ = v/ν = 440/220 = 2 m
The wavelength is 2 meters.
The time interval between successive compressions is the time period (T) of the wave.
T = 1/ν = 1/500 = 0.002 s or 2 ms
Intensity is the amount of sound energy passing each second through unit area. It is an objective physical quantity. Loudness is a subjective measure of how our ears perceive the intensity of sound. Two sounds of equal intensity may be perceived as having different loudness by our ears.
Sound travels fastest in iron, then water, and slowest in air. At 25°C, the speeds are approximately: iron - 5950 m/s, water - 1498 m/s, air - 346 m/s.
Ceilings of concert halls are curved to ensure that sound, after reflection, reaches all corners of the hall evenly. This helps in distributing sound uniformly throughout the audience area.
The audible range for the average human ear is from about 20 Hz to 20,000 Hz (20 kHz).
(a) Infrasound: Frequencies below 20 Hz
(b) Ultrasound: Frequencies above 20,000 Hz (20 kHz)
Sound is a form of energy that produces a sensation of hearing in our ears. It is produced by vibrating objects. When an object vibrates, it sets the particles of the surrounding medium into vibration, creating compressions and rarefactions that propagate as sound waves.
When a vibrating object moves forward, it pushes and compresses the air in front of it, creating a region of high pressure called compression. When it moves backward, it creates a region of low pressure called rarefaction. As the object continues to vibrate, a series of compressions and rarefactions is created in the air, forming a sound wave that propagates through the medium.
Sound waves are called longitudinal waves because the particles of the medium vibrate parallel to the direction of wave propagation. The particles move back and forth in the same direction that the wave is traveling, creating regions of compression and rarefaction.
The quality or timbre of sound helps identify your friend's voice. Quality is that characteristic of sound which enables us to distinguish between different sounds having the same pitch and loudness.
This happens because light travels much faster than sound. Light travels at about 3×10^8 m/s, while sound travels at only about 340 m/s in air. Therefore, we see the flash almost instantly, but the sound takes time to reach us.
Using the formula: λ = v/ν
For 20 Hz: λ = 344/20 = 17.2 m
For 20,000 Hz: λ = 344/20000 = 0.0172 m or 1.72 cm
The wavelengths range from 17.2 m to 1.72 cm.
Speed of sound in aluminium = 6420 m/s (from table)
Speed of sound in air = 346 m/s (from table)
Time = Distance/Speed
Since distance is same for both:
Ratio = Time in air / Time in aluminium = (d/346) / (d/6420) = 6420/346 ≈ 18.55
Sound takes about 18.55 times longer to travel through air than through aluminium.
Frequency = 100 Hz means 100 vibrations per second
Vibrations in a minute = 100 × 60 = 6000 vibrations
Yes, sound follows the same laws of reflection as light:
1. The angle of incidence is equal to the angle of reflection.
2. The incident sound wave, the reflected sound wave, and the normal to the reflecting surface at the point of incidence all lie in the same plane.
Yes, but the minimum distance required to hear a distinct echo may be different. On a hotter day, the speed of sound increases (as speed of sound increases with temperature), so the time taken for sound to travel to the obstacle and back decreases. This might affect whether we hear a distinct echo or not, depending on the actual distance.
1. Stethoscope: Used by doctors to listen to sounds produced within the body. It works on multiple reflections of sound.
2. Megaphones or loudhailers: Designed to send sound in a particular direction without spreading it in all directions, using reflection.
Time for stone to fall: s = ½gt² → 500 = ½ × 10 × t² → t² = 100 → t = 10 s
Time for sound to travel up: t = distance/speed = 500/340 ≈ 1.47 s
Total time = 10 + 1.47 = 11.47 s
The splash is heard after approximately 11.47 seconds.
Wavelength = 1.5 cm = 0.015 m
Frequency = Speed/Wavelength = 339/0.015 = 22,600 Hz = 22.6 kHz
This frequency is above the audible range for humans (20 Hz - 20 kHz), so it will not be audible to most people.
Reverberation is the persistence of sound in a hall due to repeated reflections from walls, ceiling, and other surfaces. It can be reduced by using sound-absorbent materials on the walls and ceiling, such as compressed fibreboard, rough plaster, draperies, and carpets.
Loudness is the subjective measure of the intensity of sound as perceived by the human ear. It depends on:
1. The amplitude of the sound wave - greater amplitude means louder sound
2. The sensitivity of the human ear - our ears are more sensitive to some frequencies than others
3. The distance from the source - loudness decreases with distance
Ultrasound is used for cleaning by placing objects in a cleaning solution and sending ultrasonic waves into the solution. The high frequency waves create microscopic bubbles that implode, generating strong cleaning action that dislodges dirt, grease, and contaminants from hard-to-reach places.
Ultrasound waves are passed through the metal block. If there is a defect like a crack or hole, the ultrasound waves get reflected from the defective location. Detectors are used to identify these reflected waves. The pattern of reflected waves helps locate and identify the size and nature of the defect inside the metal block.